Intraacinar profiles of alcohol dehydrogenase and aldehyde dehydrogenase activities in human liver

Sex and gender-related differences in alcohol use and its consequences: Contemporary knowledge and future research considerations

AIMS

To review the contemporary evidence reflecting male/female differences in alcohol use and its consequences along with the biological (sex-related) and psycho-socio-cultural (gender-related) factors associated with those differences.

METHODS

MEDLINE, PubMed, Web of Science, SCOPUS, PsycINFO, and CINAHL databases were searched for relevant publications, which were subsequently screened for the presence/absence of pre-specified criteria for high quality evidence.

RESULTS

Compared to men, more women are lifetime abstainers, drink less, and are less likely to engage in problem drinking, develop alcohol-related disorders or alcohol withdrawal symptoms. However, women drinking excessively develop more medical problems. Biological (sex-related) factors, including differences in alcohol pharmacokinetics as well as its effect on brain function and the levels of sex hormones may contribute to some of those differences. In addition, differences in alcohol effects on behavior may also be driven by psycho-socio-cultural (gender-related) factors. This is evident by variation in the magnitude of differences in alcohol use between countries, decreasing difference in the rates of alcohol consumption in recent generations and other findings. Evidence indicates that both sex and gender-related factors are interacting with alcohol use in complex manner, which differentially impacts the risk for development of the behavioral or medical problems and alcohol use disorders in men and women.

CONCLUSIONS

Discovery of the mechanisms underlying biological (sex-related) as well as psycho-socio-cultural (gender-related) differences in alcohol use and related disorders is needed for development of personalized recommendations for prevention and treatment of alcohol use disorders and related problems in men and women.

Pregnane X Receptor-Humanized Mice Recapitulate Gender Differences in Ethanol Metabolism but Not Hepatotoxicity

Both human and rodent females are more susceptible to developing alcoholic liver disease following chronic ethanol (EtOH) ingestion. However, little is known about the relative effects of acute EtOH exposure on hepatotoxicity in female versus male mice. The nuclear receptor pregnane X receptor (PXR; NR1I2) is a broad-specificity sensor with species-specific responses to toxic agents. To examine the effects of the human PXR on acute EtOH toxicity, the responses of male and female PXR-humanized (hPXR) transgenic mice administered oral binge EtOH (4.5 g/kg) were analyzed. Basal differences were observed between hPXR males and females in which females expressed higher levels of two principal enzymes responsible for EtOH metabolism, alcohol dehydrogenase 1 and aldehyde dehydrogenase 2, and two key mediators of hepatocyte replication and repair, cyclin D1 and proliferating cell nuclear antigen. EtOH ingestion upregulated hepatic estrogen receptor α, cyclin D1, and CYP2E1 in both genders, but differentially altered lipid and EtOH metabolism. Consistent with higher basal levels of EtOH-metabolizing enzymes, blood EtOH was more rapidly cleared in hPXR females. These factors combined to provide greater protection against EtOH-induced liver injury in female hPXR mice, as revealed by markers for liver damage, lipid peroxidation, and endoplasmic reticulum stress. These results indicate that female hPXR mice are less susceptible to acute binge EtOH-induced hepatotoxicity than their male counterparts, due at least in part to the relative suppression of cellular stress and enhanced expression of enzymes involved in both EtOH metabolism and hepatocyte proliferation and repair in hPXR females.

β-catenin is essential for ethanol metabolism and protection against alcohol-mediated liver steatosis in mice

The liver plays a central role in ethanol metabolism, and oxidative stress is implicated in alcohol-mediated liver injury. β-Catenin regulates hepatic metabolic zonation and adaptive response to oxidative stress. We hypothesized that β-catenin regulates the hepatic response to ethanol ingestion. Female liver-specific β-catenin knockout (KO) mice and wild-type (WT) littermates were fed the Lieber-Decarli liquid diet (5% ethanol) in a pairwise fashion. Liver histology, biochemistry, and gene-expression studies were performed. Plasma alcohol and ammonia levels were measured using standard assays. Ethanol-fed (EtOH) KO mice exhibited systemic toxicity and early mortality. KO mice exhibited severe macrovesicular steatosis and 5 to 6-fold higher serum alanine aminotransferase and aspartate aminotransferase levels. KO mice had a modest increase in hepatic oxidative stress, lower expression of mitochondrial superoxide dismutase (SOD2), and lower citrate synthase activity, the first step in the tricarboxylic acid cycle. N-Acetylcysteine did not prevent ethanol-induced mortality in KO mice. In WT livers, β-catenin was found to coprecipitate with forkhead box O3, the upstream regulator of SOD2. Hepatic alcohol dehydrogenase and aldehyde dehydrogenase activities and expression were lower in KO mice. Hepatic cytochrome P450 2E1 protein levels were up-regulated in EtOH WT mice, but were nearly undetectable in KO mice. These changes in ethanol-metabolizing enzymes were associated with 30-fold higher blood alcohol levels in KO mice.

CONCLUSION

β-Catenin is essential for hepatic ethanol metabolism and plays a protective role in alcohol-mediated liver steatosis. Our results strongly suggest that integration of these functions by β-catenin is critical for adaptation to ethanol ingestion in vivo.

Sex differences in hepatic gluconeogenic capacity after chronic alcohol consumption

Alcohol-induced hypoglycemia has traditionally been attributed to the amount of ethanol consumed rather than any inherent decline in glucose output capacity by the gluconeogenic organs and/or an increase in skeletal muscle glucose uptake. Further, while the potential for sex differences that might impact glucose homeostasis following chronic alcohol consumption has been recognized, direct evidence has been noticeably absent. This paper will provide a brief review of past and present reports of the potential for sex differences in glucose homeostasis following chronic ethanol consumption. This paper will also provide direct evidence from our laboratory demonstrating sex differences from chronic alcohol consumption resulting in a decrement in glucose appearance and more importantly, a specific decline in hepatic gluconeogenic (HGN) capacity in the absence and presence of ethanol. All our studies involved 8 weeks of chronic alcohol consumption in male and female Wistar rats, as well as a 24 to 48 hour fast to deplete hepatic glycogen stores. Under the conditions of chronic alcohol consumption and an acute dose of ethanol, we provide in vivo evidence of an early decline in whole body glucose appearance in females fed an ethanol diet compared to controls. While the decline was also observed in males fed the alcohol diet, it occurred much later compared to ethanol fed females. The site for the decline in whole body glucose production (i.e., either the kidneys or the liver) was beyond the scope of our prior in vivo study. In a follow-up study using the in situ perfused liver preparation, we provide additional evidence for a specific reduction in HGN capacity from lactate in ethanol fed females compared to ethanol fed males in the absence of alcohol in the perfusion medium. Finally, employing the isolated hepatocyte technique, we report decrements in HGN from lactate in ethanol fed females compared to ethanol fed males in the presence of ethanol in the incubation medium. The mechanism for the specific decline in HGN within the liver of ethanol fed females remains to be determined. To the extent that our observations in animals can be extrapolated to humans, we conclude that alcoholic women are more susceptible to ethanol-induced hypoglycemia compared to alcoholic men.

Alcohol-induced suppression of gluconeogenesis is greater in ethanol fed female rat hepatocytes than males

The impact of alcohol-induced suppression on hepatic gluconeogenesis (HGN) after chronic ethanol consumption between males and females is unknown. To determine the effects of chronic alcohol consumption (8 weeks) on HGN, the isolated hepatocyte technique was used on 24 h fasted male and female Wistar rats. Livers were initially perfused with collagenase and the hepatocytes were isolated. Aliquots of the cell suspension were placed in Krebs-Henseleit buffer and incubated for 30 min with lactate, [U -14C]lactate, and nine different concentrations of ethanol (EtOH). Dose-effect curves were generated for the determination of maximal and half-maximal alcohol-induced inhibition on HGN. There was no significant difference in HGN (lactate only and no EtOH) between males and females fed the control diet (88.5 +/- 5.1 nmol/mg protein/30 min). Similarly, the HGN (lactate only and no EtOH) in males fed the ethanol diet (ME) were not significantly different (82.8 +/- 3.5 nmol/mg protein/30 min) compared to controls. In contrast, the females chronically fed the ethanol diet (FE) had significantly (P < .05) lower HGN (67.8 +/- 4.6 nmol/mg protein/30 min) compared to both ME and controls. With alcohol in the incubation medium, the HGN significantly (P<.05) declined in all groups. While alcohol suppressed HGN to a larger (P < .05) extent in ME (45.8 +/- 3.7 nmol/mg protein/30 min) compared to controls (64.0 +/- 3.8 nmol/mg protein/30 min), the inhibition was even greater (P < .05) in FE (32.7 +/- 3.2 nmol/mg protein/30 min). The more pronounced effect of chronic alcohol consumption on HGN in the presence of ethanol in female hepatocytes was supported by the concomitant decreases (P < .05) in 14C-lactate incorporation into 14C-glucose, lactate uptake, and 14C-lactate uptake. The results suggest that chronic alcohol consumption elicits a greater reduction on HGN in the presence of ethanol in the hepatocytes of females compared to males.

Opposing effects of chronic alcohol consumption on hepatic gluconeogenesis for female versus male rats

BACKGROUND

The impact of chronic alcohol consumption on hepatic gluconeogenesis (HGN) between males and females is unknown. To determine the effects of chronic alcohol consumption (8 weeks) on HGN, the isolated liver perfusion technique was used on 24-hr-fasted male and female Wistar rats.

METHODS

After surgical isolation, livers were perfused (single pass) for 30 min with Krebs-Henseleit bicarbonate buffer and fresh bovine erythrocytes with no added substrate (washout period). After the washout period, livers were perfused with lactate (10 mM) and [U-14C]lactate (15,000 dpm/ml) using the recirculation method.

RESULTS

There was no significant difference in HGN between males and females fed the control diet. In contrast, the females chronically fed the ethanol diet (FE) had significantly lower HGN rates (2.73 +/- 0.37 micromol/min x g liver protein(-1)), whereas males fed the ethanol diet (ME) had significantly higher HGN rates (4.99 +/- 0.45 micromol/min x g liver protein(-1)) than controls (3.83 +/- 0.34 micromol/min x g liver protein(-1)). Concomitant decreases were also observed for both 14C-lactate incorporation into 14C-glucose and rates of lactate uptake for FE, while corresponding increases were observed for 14C-lactate incorporation into 14C-glucose for ME. The livers from ME were able to convert a greater percentage of the lactate into glucose, resulting in the elevation in gluconeogenic capacity.

CONCLUSION

Chronic alcohol consumption lowers the hepatic gluconeogenic capacity from lactate in females and elevates HGN in males.

Heterogenic response of the liver parenchyma to ethanol studied in the bivascularly perfused rat liver

Zonation of ethanol oxidation and metabolic effects along the hepatic acini were investigated in the bivascularly perfused liver of fed rats. Ethanol was infused into the hepatic artery in antegrade and retrograde perfusion. Inhibition of glycolysis by ethanol, expressed as micromol min(-1) (ml accessible cell space)(-1), was more pronounced in the retrograde mode; the retrograde/antegrade ratio was equal to 1.63 for an ethanol infusion rate of 37.5 micromol min(-1) g(-1). Stimulation of oxygen uptake by ethanol was more pronounced in the retrograde mode; the retrograde/antegrade ratio was equal to 1.77. Diminution of the citrate cycle caused by ethanol was more pronounced in the retrograde mode; the retrograde/antegrade ratio was equal to 1.46. Transformation of arterially infused ethanol into acetate was more pronounced in retrograde perfusion; the retrograde/antegrade ratio was equal to 1.63. The increments in glucose release (glycogenolysis) caused by ethanol in the antegrade and retrograde modes were similar. It was assumed that the changes caused by arterially infused ethanol in retrograde and antegrade perfusion closely reflect a significant part of the periportal parenchyma and an average over the whole liver parenchyma, respectively. Under such assumptions it can be concluded that, in the perfused liver from fed rats, four related parameters predominate in the periportal region: ethanol oxidation, glycolysis inhibition, oxygen uptake stimulation and citrate cycle inhibition. One of the main causes for this predominance could be the malate/aspartate shuttle, which operates more rapidly in the periportal area and is essential for NADH oxidation.

Chronic alcohol consumption yields sex differences in whole-body glucose production in rats

AIMS

The effects of chronic alcohol consumption (8 weeks) on glucose kinetics, in the absence (water, 4 g/kg) and presence of an acute ethanol dose (4 g/kg), were examined in 48 h fasted male and female Wistar rats.

METHODS

Primed continuous infusions of [6-3H]- and [U-14C]glucose were employed to assess rates of glucose appearance (Ra), glucose disappearance (Rd), and apparent glucose carbon recycling.

RESULTS

After injecting the male and female controls with water, there were no significant alterations in glucose kinetics. Compared to controls, chronic alcohol-fed female animals (injected with water) demonstrated significantly lower: glucose Ra, blood glucose concentration, and apparent glucose carbon recycling for a majority of the experimental period. In separate groups injected with ethanol, the glucose Ra fell by 31% for male rats fed the control diet (MC), 43% for male rats fed the ethanol diet (ME), 29% for female rats fed the control diet (FC), and 42% for female rats fed the ethanol diet (FE). Further, compared to controls (MC and FC), the blood glucose concentration was significantly lower prior to and following the ethanol injection for FE. In addition, FE animals had significantly lower rates of glucose Ra and glucose carbon recycling compared to controls prior to and after the ethanol injection. ME animals demonstrated similar declines in glucose Ra (compared to FE), but only after the ethanol injection. Conversely, ME were able to match the decrease in glucose Ra with comparable declines in glucose Rd resulting in blood glucose concentrations that did not differ from controls.

CONCLUSIONS

Chronic alcohol consumption results in sex differences in whole-body glucose production and glucose regulation.

Gender-related differences in hepatic activity of alcohol dehydrogenase isoenzymes and aldehyde dehydrogenase in humans

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which are most abundant in the liver, are the main enzymes involved in ethanol metabolism in humans. Gender-related differences in total liver ADH and ALDH activity among different animal species have been observed in many studies. We measured total ADH and ALDH activity, and the activity of class I-IV ADH in the livers of male and female patients. Total ADH and class I and II ADH activities were significantly higher in males than in females (P=0.0052, P=0.0074, P=0.020, respectively). Class III and IV ADH and total ALDH activities were not significantly different between the genders (P=0.2917, P=0.0590, P=0.2940, respectively). The results of our study clearly show that there is a difference in enzymatic activity between male and female patients for those isoenzymes that actively participate in ethanol oxidation in the liver (class I and II ADH), although the main form of ADH in this organ is class III ADH.

Species variations in cutaneous alcohol dehydrogenases and aldehyde dehydrogenases may impact on toxicological assessments of alcohols and aldehydes

Alcohol dehydrogenase (ADH; EC. 1.1.1.1) and aldehyde dehydrogenase (ALDH; EC 1.2.1.3) play important roles in the metabolism of both endogenous and exogenous alcohols and aldehydes. The expression and localisation patterns of ADH (1-3) and ALDH (1-3) were investigated in the skin and liver of the mouse (BALB/c and CBA/ca), rat (F344) and guinea-pig (Dunkin-Hartley), using Western blot analysis and immunohistochemistry with class-specific antisera. ALDH2 expression and localisation was also determined in human skin, while ethanol oxidation, catalysed by ADH, was investigated in the mouse, guinea-pig and human skin cytosol. Western blot analysis revealed that ADH1, ADH3, ALDH1 and ALDH2 were expressed, constitutively, in the skin and liver of the mouse, rat and guinea-pig. ADH2 was not detected in the skin of any rodent species/strain, but was present in all rodent livers. ALDH3 was expressed, constitutively, in the skin of both strains of mouse and rat, but was not detected in guinea-pig skin and was absent in all livers. Immunohistochemistry showed similar patterns of expression for ADH and ALDH in both strains of mouse, rat, guinea-pig and human skin sections, with localisation predominantly in the epidermis, sebaceous glands and hair follicles. ADH activity (apparent V(max), nmoles/mg protein/min) was higher in liver (6.02-16.67) compared to skin (0.32-1.21) and lower in human skin (0.32-0.41) compared to mouse skin (1.07-1.21). The ADH inhibitor 4-methyl pyrazole (4-MP) reduced ethanol oxidation in the skin and liver in a concentration dependent manner: activity was reduced to approximately 30-40% and approximately 2-10% of the control activity, in the skin and liver, respectively, using 1 mM 4-MP. The class-specific expression of ADH and ALDH enzymes, in the skin and liver and their variation between species, may have toxicological significance, with respect to the metabolism of endogenous and xenobiotic alcohols and aldehydes.

Sex-dependent induction of alcohol dehydrogenase activity in rats

The glycolethers 2-methoxyethanol (2-ME), 2-ethoxyethanol (2-EE), and 2-butoxyethanol are widely used organic solvents with teratogenic, spermatotoxic, and hematotoxic effects due to the respective alkoxyacetic acid metabolites formed via alcohol dehydrogenase (ADH). ADH displays sexually dimorphic activities in adult rats, and is probably at least in part under the control of testosterone. The aim of this study was to investigate whether induction of ADH is also sex-dependent. Ethanol, 2-ME, and 2-EE were tested as inducers of hepatic and gastric ADH in female, male, and castrated male rats. The activity of hepatic ADH was higher in female than in male rats, while the activity of gastric ADH was higher in male than in female rats. The activities of ADH increased with increasing chain length of the glycolethers and alcohols. Castration of male rats led to a female pattern of ADH activity, i.e. increased activity of hepatic ADH and decreased activity of gastric ADH. Ethanol had no inducing effect on hepatic ADH in either male or female rats. 2-ME and 2-EE caused an increase in the activity of hepatic ADH in male and castrated male rats only. The present data demonstrate a different expression of ADH isoenzymes in male and female rats, and a sex-dependent induction of ADH isoenzymes. The different possible regulatory mechanisms for the different ADH isoenzymes require further investigation.

Physiologically based pharmacokinetic model for chronic inhalation of 2-butoxyethanol

2-Butoxyethanol (2BE) is used extensively in the production of cleaning agents and as a general solvent. It is primarily metabolized in the liver to 2-butoxyacetic acid (2BAA), which is excreted in urine. The objective of this study was to develop a physiologically based pharmacokinetic (PBPK) model describing the toxicokinetic behavior of 2BE and 2BAA in different species following repeated, long-term exposures. The PBPK model was first developed for short-term 2BE exposure to male rats. Allometric scaling was employed to estimate physiological and biochemical model parameters based on body weight. To accommodate differences in 2BE toxicokinetics in female rats, a higher Vmax for 2BE metabolism to 2BAA, higher plasma protein binding sites for 2BAA, and lower Vmax for 2BAA excretion through the kidney were incorporated into the model. For mice, a higher Vmax for 2BE metabolism to 2BAA for both sexes and higher plasma protein binding sites for 2BAA for female mice were also incorporated into the model. Subsequently, the model was expanded to simulate 2BE and 2BAA toxicokinetics for long-term, repeated exposures by incorporating time-dependent changes in model parameters. To reflect physiological/biochemical changes in animals during a chronic exposure, parameters for cardiac output, body composition, metabolic capacity, protein binding, or capacity of renal excretion were adjusted over time depending on species and sex. Sensitivity analysis was performed to better understand how sensitive model responses were to uncertainties in input parameters. The resulting PBPK model was used to simulate toxicokinetic data acquired during a 2-year inhalation toxicity and carcinogenicity study in male and female F344/N rats and B6C3F1 mice.

Toxicokinetics of inhaled 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in F344 rats and B6C3F1 mice

2-Butoxyethanol (2BE) is used extensively in the production of cleaning agents and solvents. It is primarily metabolized in the liver to 2-butoxyacetic acid (2BAA), which is believed to be responsible for 2BE toxicities associated with hemolysis of red blood cells. The objective of the study was to characterize the systemic disposition of 2BE and 2BAA in rats and mice during 2-year 2BE inhalation toxicity studies. Male and female F344 rats and B6C3F1 mice (6-7 weeks old) were exposed to target 2BE concentrations of 0, 31.2, 62.5, or 125 ppm (rats), or 0, 62.5, 125, or 250 ppm (mice), by whole-body inhalation for 6 h/day, 5 days/week for up to 18 months. Postexposure blood samples were collected after 1 day, 2 weeks, and 3, 6, 12, and 18 months of exposure. Postexposure 16-h urine samples were collected after 2 weeks and 3, 6, 12, and 18 months of exposure. A separate set of mice was kept in the control chamber and exposed to 2BE for 3 weeks when they were approximately 19 months old. Postexposure blood samples were collected after 1 day and 3 weeks of exposure and 16-h urine samples were collected after 2 weeks of exposure from these aged mice. Blood samples were analyzed for both 2BE and 2BAA and urine samples were analyzed for 2BAA using GC/MS, and their kinetic parameters were estimated through the curve-fitting method using SAS. Systemically absorbed 2BE was rapidly cleared from blood (t1/2-RAT < 10 min; t1/2-MOUSE < 5 min after the 1-day exposure) independent of exposure concentration. Proportional increases in AUC2BE relative to increases in exposure concentration indicated linear 2BE kinetics. In contrast, the rate of 2BAA elimination from blood decreased as the exposure concentration increased. Nonproportional increases in AUC2BAA also indicated that 2BAA is eliminated following dose-dependent, nonlinear kinetics. Overall, mice eliminated both 2BE and 2BAA from blood faster than rats. Sex-related differences in 2BAA elimination were most significant with rats, in that females were less efficient in clearing 2BAA from the blood. Differences in renal excretion of 2BAA are possibly responsible for the sex-related difference in the 2BAA blood profiles in rats. As exposure continued, the rates of elimination for both 2BE and 2BAA decreased in both species, resulting in longer residence times in the blood. When 19-month-old naive mice were exposed to 125 ppm, 2BE was rapidly cleared from the systemic circulation, exhibiting clearance profiles similar to young mice. However, old mice eliminated 2BAA from blood > 10 times slower than young mice after 1-day of exposure. This delayed elimination of 2BAA in old mice was less obvious after 3 weeks of exposure, suggesting that there might be other factors in addition to the age of animals that could influence the apparent difference in 2BAA kinetics between old and young mice. It was concluded that the elimination kinetics of 2BE and 2BAA following repeated 2BE exposure appear to be dependent on species, sex, age, time of exposure, as well as the exposure concentration.

Ultrathin-layer zone electrophoresis of alcohol dehydrogenase in partly rehydrated polyacrylamide gels: an alternative to starch gel electrophoresis

A highly sensitive electrophoretic technique for the separation of alcohol dehydrogenase isoenzymes by zone electrophoresis in partly rehydrated polyacrylamide gels is described. Five hundred microm thin polyacrylamide gels are polymerized under standardized conditions. After polymerization the gels are washed thoroughly with distilled water to remove any unreacted monomers, catalysts or still soluble polymers. The washed gels are then impregnated with 0.5% Tween 20 and dried. Before electrophoresis the dry gels are rehydrated to a thickness of 250 microm, which makes up 50% of the original gel volume. Rehydration is carried out by use of a degassed buffer solution. This method permits the demonstration of the isoenzymes of alcohol-dehydrogenase class I and II in man and allows quantitative determination.

The role of liver alcohol dehydrogenase isoenzymes in the oxidation of glycolethers in male and female rats

The glycolethers 2-methoxyethanol (2-ME), 2-ethoxyethanol (2-EE), and 2-butoxyethanol (2-BE) are used as solvents and have teratogenic, spermatotoxic, and hematotoxic effects. These glycolethers are oxidized to their corresponding alkoxyacetic acids, probably by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). This metabolic conversion of the glycolethers is a prerequisite for development of toxicity, as the toxic effects have been shown to be due to the alkoxyacetic acid metabolites. Three isoenzymes of ADH have been detected in rat tissues. The liver contains two of these isoenzymes, ADH-2 and ADH-3. It has also been shown that the activity level of ADH is strongly sex dependent, with higher activity in females than in males. In the present study, we have investigated whether one or both of the ADH isoenzymes in male and female rat livers were able to oxidize 2-ME, 2-EE, and 2-BE and whether one or both of the ADH isoenzymes in male rat liver were able to oxidize 2-pentyloxyethanol and 2-hexyloxyethanol. Our results indicated that only the ADH-3 isoenzyme effectively oxidized the glycolethers in rat liver. Both ADH-2 and ADH-3 were able to oxidize medium chain aliphatic alcohols with a chain length corresponding to the glycolethers. The activity of ADH is higher in female than in male rat liver. However, it was the same ADH isoenzyme (ADH-3) that oxidized the different glycolethers tested in both male and female rat livers, and the substrate specificity was 2-BE > 2-EE > 2-ME.

Metabolism of ethanol and some associated adverse effects on the liver and the stomach

Current knowledge of alcohol oxidation and its effects on hepatic metabolism and its toxicity are summarized. This includes an evaluation of the relationship of the level of consumption to its interaction with nutrients (especially retinoids, carotenoids, and folate) and the development of various stages of liver disease. Ethanol metabolism in the stomach and its link to pathology and Helicobacter pylori is reviewed. Promising therapeutic approaches evolving from newly gained insight in the pathogenesis of medical complications of alcoholism are outlined. At present, the established approach for the prevention and treatment of alcoholism are outlined. At present, the established approach for the prevention and treatment of alcoholic liver injury is to control alcohol abuse, with the judicial application of selective antioxidant therapy, instituted at early stages, prior to the social or medical disintegration of the patient, and associated with antiinflammatory agents at the acute phase of alcoholic hepatitis. In addition, effective antifibrotic therapy may soon become available.

Heterogeneity of kinetic parameters of enzymes in situ in rat liver lobules

In the present review, metabolic compartmentation in liver lobules is discussed as being dynamic and more complex than thus far assumed on the basis of numbers of mRNA or protein molecules or the capacity (zero-order activity) of enzymes. Isoenzyme distribution patterns and local kinetic parameters of enzymes may vary over the different zones of liver lobules. As a consequence, metabolic fluxes in vivo at physiological substrate concentrations may be completely different from those that are assumed on the basis of the number of molecules or the capacity of enzymes present in zones of liver lobules. For a more correct estimation of the levels of metabolic processes in the different compartments of liver tissue, local kinetic parameters and substrate concentrations have to be determined to calculate local metabolic fluxes. Direct measurements of metabolic fluxes in vivo with the use of noninvasive techniques is a promising alternative and the techniques will become increasingly important in future metabolic research.

Analysis of enzyme reactions in situ

Estimations of metabolic rates in cells and tissues and their regulation on the basis of kinetic properties of enzymes in diluted solutions may not be applicable to intact living cells or tissues. Enzymes often behave differently in living cells because of the high cellular protein content that can lead to homologous and heterologous associations of protein molecules. These associations often change the kinetics of enzymes as part of post-translational regulation mechanisms. An overview is given of these interactions between enzyme molecules or between enzyme molecules and structural elements in the cell, such as the cytoskeleton. Biochemical and histochemical methods are discussed that have been developed for in vivo and in situ analyses of enzyme reactions, particularly for the study of effects of molecular interactions. Quantitative (histochemical) analysis of local enzyme reactions or fluxes of metabolites has become increasingly important. At present, it is possible to calculate local concentrations of substrates in cells or tissue compartments and to express local kinetic parameters in units that are directly comparable with those obtained by biochemical assays of enzymes in suspensions. In situ analysis of the activities of a number of enzymes have revealed variations in their kinetic properties (Km and Vmax) in different tissue compartments. This stresses the importance of in vivo or in situ analyses of cellular metabolism. Finally, histochemical determinations of enzyme activity in parallel with immunohistochemistry for the detection of the total number of enzyme molecules and in situ hybridization of its messenger RNA allow the analysis of regulation mechanisms at all levels between transcription of the gene and post-translational activity modulation.

Genetic polymorphism and activities of human colon alcohol and aldehyde dehydrogenases: no gender and age differences

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isoenzyme patterns from 69 (men, 47; women, 22) surgical colon mucosal specimens were identified by agarose isoelectric focusing. gamma-ADH was found to be the predominant form in the mucosa, whereas only beta-ADH was detectable in the muscle layer. ALDH1, ALDH2, and ALDH3 were detectable in the mucosa, with cytosolic ALDH1 being the major form. At pH 7.5, the ADH activities in the colon mucosae with the homozygous phenotype (exhibiting gamma 1 gamma 1) and the heterozygous phenotype (exhibiting gamma 1 gamma 1, gamma 1, gamma 2, gamma 2, gamma 2) were determined to be 183 +/- 13 and 156 +/- 30 nmol/min/g tissue, respectively. The ALDH activities in the ALDH2-active and ALDH2-inactive phenotypes were determined to be 40.2 +/- 2.3 and 34.6 +/- 2.0 nmol/min/g tissue, respectively. The lack of significant difference in the ALDH activities between these two phenotypic groups can be attributed to the very low expression of the mitochondrial ALDH2 in the colon mucosa. No significant differences in the ADH or the ALDH activities were found between the men and women studied and between the three age groups (20-40, 49-70, and 72-83 years). The ascending, transverse, descending, and sigmoid colons exhibited similar ADH and ALDH activities. The isoenzyme patterns of ADH and ALDH remained unaltered in colon carcinomas, except that a significant reduction of the enzyme activities was found in the cancer tissue as compared with the adjacent normal portions. it is concluded that human colon mucosa exhibits significant amounts of ethanol- and acetaldehyde-oxidizing activities.

The intramucosal distribution of gastric alcohol dehydrogenase and aldehyde dehydrogenase activity in rats

Using qualitative and microquantitative histo-chemical techniques, alcohol dehydrogenase and aldehyde dehydrogenase activity was studied in the gastric mucosa of male and female rats. Alcohol dehydrogenase was demonstrated by staining reactions with maximum activity in surface and neck cells and with clearly weaker activity also in parietal cells. Aldehyde dehydrogenase could be detected in surface and neck cells, and also to a comparable degree in the parietal cells. Quantitative analyses of microdissected samples yielded high values for alcohol dehydrogenase activity exclusively in the superficial part of the gastric mucosa, whereas low-Km aldehyde dehydrogenase activity showed a decreasing gradient from the surface to the deeper parts of the mucosa. Sex differences could not be confirmed.

Sex differences in gastric alcohol dehydrogenase activity in Sprague-Dawley rats

The effects of sex differences and of fasting on gastric alcohol dehydrogenase activity were determined in Sprague-Dawley rats. Gastric alcohol dehydrogenase activity and enzyme protein levels were higher in female than in male rats. Ovariectomy and orchiectomy had no effect on alcohol dehydrogenase and did not alter the sex difference in enzyme activity. Fasting decreased the enzyme activity more in female than in male rats, abolishing the sex difference. Serum gastrin levels measured in female rats decreased on fasting and returned to normal levels within 24 hours of refeeding. Short- and long-term administration of pentagastrin to fasted and fed female rats did not affect the enzyme activity or enzyme protein level, except for a transient increase in enzyme activity but not in enzyme protein level 12 hours after administration to fasted fats. Omeprazole, which increased serum gastrin levels and decreased enzyme activity but not enzyme protein levels, was found to be a competitive inhibitor of the enzyme with a Ki of 0.40 mmol/L. The mechanisms for the sex differences and changes with fasting in rat gastric alcohol dehydrogenase activity remain unknown.

Metabolic zonation of the liver: regulation and implications for liver function

Liver parenchyma shows a remarkable heterogeneity of the hepatocytes along the porto-central axis with respect to ultrastructure and enzyme activities resulting in different cellular functions within different zones of the liver lobuli. According to the concept of metabolic zonation, the spatial organization of the various metabolic pathways and functions forms the basis for the efficient adaptation of liver metabolism to the different nutritional requirements of the whole organism in different metabolic states. The present review summarizes current knowledge about this heterogeneity, its development and determination, as well as about its significance for the understanding of all aspects of liver function and pathology, especially of intermediary metabolism, biotransformation of drugs and zonal toxicity of hepatotoxins.

Modern approach to alcoholic liver disease

The pathogenesis of alcoholic liver disease is unclear. The recent literature on pathogenic factors, including direct effects of ethanol and its proximate metabolite acetaldehyde, associated nutritional factors, the formation of acetaldehyde-protein adducts, associated immune alterations, and the potential for liver injury due to coexisting hepatitis virus infection, is highlighted. The therapy of patients with advanced alcoholic liver injury, especially alcoholic hepatitis, is also controversial. It seems reasonable that all patients should receive adequate nutrition even if parenteral or enteral supplementation is required. Corticosteroid administration may benefit those patients with alcoholic hepatitis who have coexisting spontaneous hepatic encephalopathy and no gastrointestinal bleeding. For patients with complications from end-stage alcoholic cirrhosis, liver transplantation should be considered, as the patient with alcoholic cirrhosis does as well after liver transplantation as those patients with other forms of end-stage liver disease.